A resident cat and new cat should be able to smell and hear each other. You can do this by feeding both cats near the door to the isolation room so they learn to associate the smell and sound of each other with a positive experience. Doling out treats near the door is also a good idea.
After 2-3 days, some cat experts recommend switching the cats’ locations so they can get used to each others’ smells. Of course if the new cat is still tentative about walking freely around his /her space do not force this.
Many behaviorists advise rubbing the cats with the same towel to mix their scents. Use a clean sock to rub on the new cat’s face to capture her facial pheromones. Then, she instructs, leave the sock near the existing cat and let him investigate on his own.
After a few more days, the next step is to play with each of the cats near the door, building up positive associa- tions with the scent of the other cat. This play, again, helps each cat associate the other cat with a good time.
Continue feeding, playing with and giving the cats treats within view of the other cats, but don’t force it! If one cat won’t eat her food right next to the screen, try moving the food dish a few feet away, Let the cats determine how close you move the dish. If both cats are eating comfortably, try moving the dish a little closer, but don’t be afraid to start off with the food dishes ten — or more– feet apart.”
It may take time and a bit of patience but your efforts have a good chance of being rewarded in the long run when your cats become content companions in your home for life.
Set up a safe room for your cat
Set up a special isolation room for your new cat. This will provide them with a safe place to get used to their surroundings and enable you to control how they explore the new surroundings. and when your cats/dogs meet each other. The special room for your new cat should have all the trappings of home – a litter box, food/water, some cozy hiding places, a scratching post and toys. Let them hide for the initial days if that is what they need to do. This will not be forever. Let them adjust at their own pace. Enter the space but do not pull them out of hiding or grab for the cat. They will adjust and come out as soon as they know it is safe.
SLOWLY LET THE CATS SEE EACH OTHER
If all seems to be going well and your cats aren’t hissing or growling under the door at each other, after a week, you can try visually introducing the cats. Installing a screen door or even a high baby gate (that neither cat can jump over) can work. It’s helpful to have another human with you so there is one person and one cat on each side of the barrier.
MAKE THE FACE-TO-FACE INTRODUCTION
The final step in the process is to let the cats be together, face-to-face, for supervised interaction. Don’t worry if the cats completely ignore each other or hiss a bit and then walk away. It will take some time for your cats to learn that the other is a friend and not a foe. Keep watching the cats and let them take things at their own pace as long as no one is starting to bully or harass the other. You should be able to gauge how it’s going. If you sense one cat is harassing the other separate and give them more time.